Where does left over sperm goes after ejaculation? how long does it stay in the body after ejaculation? what kills the left over sperm?

Disintegrate in time: Think of sperm as a package of DNA, a battery, a motor, and a propeller. Once the battery runs out, they are "dead in the water." Inside a guy, leftover sperm probably mixes in with a bit of mucus in the urethra, or secretions from the prostate, and gets flushed out by urine. Inside a vagina, leftover sperm gets mixed in with vaginal mucus and secretions, disintegrates, and flows out the vagina.